Mycobacterium tuberculosis subsp. caprae subsp. nov.: A taxonomic study of a new member of the Mycobacterium tuberculosis complex isolated from goats in Spain

This study describes the first identification of Mycobacterium tuberculosis subsp. caprae, a new subspecies within the M. tuberculosis complex isolated from goats in Spain. Researchers examined 121 mycobacterial isolates from tuberculosis-infected goats (and one sheep and pig) using biochemical testing, gas chromatography, molecular analysis, and genetic fingerprinting. The caprine isolates displayed unusual characteristics that distinguished them from classical M. tuberculosis complex members: they were pyrazinamide-sensitive (unlike M. bovis), showed an M. tuberculosis-like pncA gene polymorphism combined with M. bovis-like sequences in other genes (katG, oxyR, gyrA), and produced distinct fingerprinting patterns with IS6110, direct repeats, and spoligotyping. These features, combined with repeated isolation from goats across multiple Spanish herds, suggested a previously unrecognized complex member. The authors formally propose M. tuberculosis subsp. caprae subsp. nov., with strain gM-1T designated as the type strain. The findings highlight that this organism may have epidemiological significance for both animal and human tuberculosis in Spain.

Key findings

• A novel subspecies, Mycobacterium tuberculosis subsp. caprae, was identified from 119 goats across multiple Spanish herds based on distinctive biochemical, genetic, and epidemiological characteristics.
• The new subspecies is pyrazinamide-sensitive (unlike M. bovis) but carries the M. tuberculosis wild-type pncA gene polymorphism, with other genes (katG, oxyR, gyrA) resembling M. bovis.
• Genetic fingerprinting using IS6110, direct repeats, and spoligotyping clearly segregated the caprine isolates from all classical M. tuberculosis complex members, forming a distinct cluster.
• The designation Mycobacterium tuberculosis subsp. caprae subsp. nov. is formally proposed, with strain gM-1T (CIP 105776T) designated as the type strain.
• This organism may play an important epidemiological role in animal and human tuberculosis transmission in Spain.